The invention relates generally to the making of color prints from a master or original.
More particularly, the invention relates to a method of and apparatus for adjusting a color density measuring unit for a master to the spectral sensitivity of the copy material on which a print of the master is to be made.
To obtain optimal exposure times for a photographic copy material when using a measuring unit which measures the color density of the master, it is necessary for the spectral sensitivity of the measuring unit to be as close as possible to the spectral sensitivity of the copy material.
To this end, the European patent application 0 420 816 discloses a photographic color copying apparatus with a measuring unit in which the spectral transmission lines of measuring filters, i.e. color filters, are shifted as a function of the angle of incidence of light on a measuring filter. The measuring filter is stationary and cooperates with at least two separate light sensors. The sensors are situated in such a manner that each receives light from a different angular range of the cone of measuring light coming from the filter. This arrangement requires a large number of sensors in order to span as large an angle as possible. Aside from the increased cost for the large number of sensors, the maxima of the spectral ranges detected by different sensors are spaced from one another by a predetermined distance. Due to the geometry of the known arrangement, this spacing cannot be reduced at will. The measuring unit is adjusted to the spectral sensitivity of a master using measurement signals from the sensor which detects the spectral region most closely approximating the spectral sensitivity of the copy material. When many different copy materials are employed, it can happen that the maximum of the spectral sensitivity of a copy material lies between the maxima of the spectral regions detected by the sensors. Color falsification can then occur.